1. Field of the Invention
The present invention relates to an organic semiconductor applicable to organic electronic devices, such as an organic thin-film solar cell, organic transistor, photosensor, and electroluminescence device.
2. Description of the Related Art
Organic semiconductors having a charge (electron or hole) transfer characteristic are expected to be applied to organic electronic devices. Because an organic electronic device is rich in flexibility; its area and weight can be expected to be enlarged and reduced, respectively; and a simple and inexpensive manufacturing method can be expected, it is considered to be a promising technique. In manufacturing a high-performance organic electronic device, high charge transfer characteristic is particularly desired. In an organic thin-film solar cell, for example, a larger current can be obtained as the charge transfer characteristic thereof is higher, thereby allowing a solar cell exhibiting a high conversion efficiency to be manufactured. In an organic transistor, for example, a flowing current becomes larger as the charge transfer characteristic thereof is higher, thereby allowing the transistor to exhibit excellent characteristics as a transistor.
As an index for the charge transfer characteristic of an organic semiconductor, charge mobility can be mentioned. The charge mobility represents the moving speed of a charge in a unit electric field. An organic semiconductor having a higher charge mobility is more excellent in a charge transfer characteristic. It is recognized that an improvement in the interaction between π-planes in an organic semiconductor is effective in improving the charge mobility thereof. It is required to extend a π-conjugated system in order to improve the interaction between π-planes. As a typical method of obtaining an extended π-conjugated system, a unit structure having a further large π-plane, such as, for example, naphthalene and anthracene, is introduced into a molecule. Also, it is known that a π-conjugated system is extended by making the electronic structure of a molecule to polarize with a unit structure, having a large difference between the electron-donating property and the electron-attracting property, being introduced into the molecule.